/*=====================================================================*
 *                   Copyright (C) 2011 Paul Mineiro                   *
 * All rights reserved.                                                *
 *                                                                     *
 * Redistribution and use in source and binary forms, with             *
 * or without modification, are permitted provided that the            *
 * following conditions are met:                                       *
 *                                                                     *
 *     * Redistributions of source code must retain the                *
 *     above copyright notice, this list of conditions and             *
 *     the following disclaimer.                                       *
 *                                                                     *
 *     * Redistributions in binary form must reproduce the             *
 *     above copyright notice, this list of conditions and             *
 *     the following disclaimer in the documentation and/or            *
 *     other materials provided with the distribution.                 *
 *                                                                     *
 *     * Neither the name of Paul Mineiro nor the names                *
 *     of other contributors may be used to endorse or promote         *
 *     products derived from this software without specific            *
 *     prior written permission.                                       *
 *                                                                     *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND              *
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,         *
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES               *
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE             *
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER               *
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,                 *
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES            *
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE           *
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR                *
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF          *
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT           *
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY              *
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE             *
 * POSSIBILITY OF SUCH DAMAGE.                                         *
 *                                                                     *
 * Contact: Paul Mineiro <paul@mineiro.com>                            *
 *=====================================================================*/

#ifndef __FRSQRT_HH__
#define __FRSQRT_HH__

namespace 
{
#ifdef __SSE__
#include <emmintrin.h>

  inline float
  rsqrtf (float x)
    {
      float rv;

      __m128 arg = _mm_load_ss (&x);
      arg = _mm_rsqrt_ss (arg);
      _mm_store_ss (&rv, arg);

      return rv;
    }
#else
#include <stdint.h>

  inline float
  rsqrtf (float x)
    {
      union { float f; uint32_t i; } vx = { x };
      union { uint32_t i; float f; } vy = { 0x5f3759df - (vx.i >> 1) };
      const float threehalfs = 1.5f;

      vy.f = vy.f * (threehalfs - (0.5f * x * vy.f * vy.f));

      return vy.f;
    }
#endif // __SSE__
}

#endif // __FRSQRT_HH__
